Answer: The word "quixotic" is most clearly defined as "impractical".
Explanation: The word "quixotic" is an adjective and<u> it is mainly used to describe someone as unnecessarily idealistic</u>. In other words, <u>"quixotic"</u>, <u>which derives from the character "Don Quixote", can be defined as "impractical and unrealistic". </u>Therefore, the adjective "rational" cannot be applied to this word. Moreover, "sentimental" and "insane" do not capture the real meaning of "quixotic" either.